1. Field of the Invention
The present invention relates to an electrophotographic printing method and, more particularly, to an electrophotographic printing method in which a charge voltage is appropriately varied depending on the print resolution or print mode.
2. Description of the Related Art
A general electrophotographic imaging system, such as a copy machine, printer or facsimile, includes a controller for controlling formation of an image, a laser scanning unit (LSU), a high-voltage power supply (HVPS), a charge roller, a photoreceptor drum serving as an organic photoconductor (OPC), a developer roller, a transfer roller, and a blade.
Under the control of the controller, the HVPS supplies a charge voltage of xe2x88x921.4 kilo Volts (kV) to the charge roller, a development voltage of xe2x88x92300 Volts (V) to the developer roller, and a transfer voltage of +2.0 kV to the transfer roller.
As the development voltage of xe2x88x92300 V is applied to the developer roller by the HVPS, toner particles which almost have a negative charge are attracted to the surface of the developer roller by frictional force acting between a toner supply roller and the developer roller. However, due to a large amount of stress between the toner supply roller and the developer roller and irregular toner particle size, toner particles having a positive charge can be applied to the surface of the developer roller. The charge roller is formed of a conductive roller having an appropriate resistance. As a voltage of xe2x88x921.4 kV is applied to the charge roller, the surface of the OPC is charged to a negative potential of xe2x88x92800 V. Under the control of the controller, the LSU scans the surface of the OPC with a beam to form an electrostatic latent image on the OPC. Here, an image area in which the electrostatic latent image is formed has a potential of xe2x88x9250 V, and a non-image area has a potential of xe2x88x92800 V.
Meanwhile, as the electrostatic latent image area of the OPC passes the developer roller, toner particles adhering to the surface of the developer roller migrate to the electrostatic latent image area of the OPC by a potential difference, so that a visible image is formed on the surface of the OPC. The visible image formed on the surface of the OPC is transferred to and printed on a paper passing through a gap, which is also called a xe2x80x9cnipxe2x80x9d, between the OPC and the transfer roller. The blade is used to mechanically remove the toner particles remaining on the surface of the OPC.
When a print command is input from a user, an image which is intended to be printed is input to an electrophotographic imaging apparatus through a personal computer (PC). The controller starts to operate (ON-state) to form a matrix of dots in accordance with the input image. A charge voltage of xe2x88x921.4 kV is applied to the charge roller under the control of the controller to charge the OPC to a potential of xe2x88x92800 V.
As the LSU scans the matrix of dots formed on the surface of the OPC with a laser beam in response to a control signal from the controller, the potential of the exposed area is changed to have a potential of xe2x88x9250 V and the non-exposed remains at a potential of xe2x88x92800 V.
When toner particles are applied to the exposed area of the OPC to form a visible image, a sheet of paper is fed through the nip formed between the transfer roller and the OPC. As a high voltage of from 500 to 3,000 V is applied to the transfer roller, the toner image formed on the OPC is transferred to the paper. The toner particles remaining on the OPC which are not transferred to the paper are removed by the blade and transferred into a recycled toner container. As the paper passes a fusing unit, a permanent image is printed on the paper by hot pressing. If it is determined to continue printing, the process returns to the first step and the above-described steps are repeated. The potential variation of the OPC is proportional to a gray pattern level variation. Assuming that the same printing conditions are applied, the gray level variation is greater for the 1 by 1 dot size than for the 4 by 4 dot size. The same result can be obtained from comparison of the printing results at resolutions of 600 dots per inch (dpi.) and 1200 dpi. In other words, because the dot size is smaller at 1200 dpi. than at 600 dpi., the gray level variation is greater at 1200 dpi. Thus, there is a problem that a desired high quality print output typically cannot be obtained.
To solve the above-described problems, it is a first object, among other objects, of the present invention to provide an electrophotographic printing method in which a charge voltage is appropriately varied depending on the print resolution.
It is a second object, among other objects, of the present invention to provide an electrophotographic printing method in which a charge voltage is appropriately varied depending on print mode.
To achieve the first object of the present invention, there is provided an electrophotographic image printing method for an electrophotographic imaging apparatus, the electrophotographic imaging apparatus including: a charge roller; a developer roller; a laser scanning unit (LSU); a transfer roller; an organic photoconductor (OPC); a power supply unit for supplying power to the charge roller, the developer roller, the LSU, the transfer roller, and the OPC; and a controller for controlling the power supply unit, the charge roller, the developer roller, the LSU, the transfer roller, and the OPC, the method comprising the steps of: (a) selecting a resolution for electrophotographic printing; (b) charging the OPC by applying to the charge roller an appropriate charge voltage depending on the selected resolution for electrophotographic printing; (c) forming an electrostatic latent image on the charged OPC by the LSU and applying toner particles adhering to the developer roller to the electrostatic latent image to form a visible image; and (d) transferring the visible image formed on the OPC to a sheet of print paper.
It is preferable that, when the resolution selected for electrophotographic printing in step (a) has a lower level, the charge voltage of step (b) is set to be higher than when the resolution selected in step (a) has a higher level.
To achieve the second object of the present invention, there is provided an electrophotographic printing method for an electrophotographic imaging apparatus, the electrophotographic imaging apparatus including: a charge roller; a developer roller; a laser scanning unit (LSU); a transfer roller; an organic photoconductor (OPC); a power supply unit for supplying power to the charge roller, the developer roller, the LSU, the transfer roller, and the OPC; and a controller for controlling the power supply unit, the charge roller, the developer roller, the LSU, the transfer roller, and the OPC, the method comprising the steps of: (a) selecting a print mode for electrophotographic printing; (b) charging the OPC by applying to the charge roller an appropriate charge voltage depending on the selected print mode for electrophotographic printing; (c) forming an electrostatic latent image on the charged OPC by the LSU and applying toner particles adhering to the developer roller to the electrostatic latent image to form a visible image; and (d) transferring the visible image formed on the OPC to a sheet of print paper.
It is preferable that the print mode selected in step (a) includes a text mode and a graphics mode, and the charge voltage applied to the charge roller of step (b) is set to be higher in the text mode than in the graphics mode.